What is the literal translation of "Lo Sirdeh Vo b'Farech"?
Targum Onkelos, Ibn Ezra: Do not subjugate him with hard work.
Having already said "Lo Sa'avod bo Avodas Aved" (in Pasuk 39), why does it repeat does the Torah find it necessary to add it here?
Why does the Pasuk add the phrase "v'Yareisa me'Elokecha"?
Rashi: Because nobody knows what is in his mind, whether the work is needed or not, other than Hashem.
Rashi writes that only Hashem knows what is Avodas Parech, i.e. unneeded. We find (verse 53) that we must stop a Nochri from making an Eved Ivri do such work! And what is Rashi's question (verse 44), who will do such work for us?!
Meshivas Nefesh: Perhaps there, Avodas Parech is hard work. However, Rashi did not say so!
Meshivas Nefesh #2: Avodas Parech includes what is unneeded, and work without a known limit 1 , e.g. 'dig under the vine until I come.' The latter is known to people, and we need slaves to do such work for us.
Rambam (Hilchos Avadim 1:6) explains so, but the Sifra and our text of Rashi implies that all of the tasks mentioned are not needed. The verse implies that all Avodas Parech is not known to others, therefore it says "v'Yareisa me'Elokecha"!
Rashi writes that Avodas Parech is unneeded. Why would a master do so, and weaken his slave without need?
Toras Moshe: A slave leaves at the end of six years, like Yetzi'as Mitzrayim. A master might think that he will not rejoice in this; sometimes he wants to remain a slave, Ki Tov Lo Imach; therefore, I will subject him to Avodas Parech, and he will rejoice to go free! The Torah forbids this 'Chasidus'; it is folly.
The master can command matters that do not weaken him, just it is frustrating to toil for no need. Perhaps he wants to pain him! Alternatively, he orders him to do unneeded work, lest he grow weak from being idle, like Rava said about workers who carry burdens (Bava Metzi'a 77a). Rava said that they prefer working to being idle, i.e. they can say so to demand their full wage if the employer retracted, but if such an Eved Ivri says that he prefers to be idle, one cannot order him to do unneeded work. Or, they prefer doing needed work to being idle,(PF)